1. Field of the Invention
The present invention relates to a solid-state image pickup device, and more particularly, to a defect compensator for a solid-state image pickup device in which a white defect or a black defect in a cell is compensated inside a charge coupled device (CCD).
2. Discussion of the Related Art
A conventional defect compensator for a solid-state image pickup device will be explained with reference to FIG. 1. FIG. 1 is a block diagram describing the components of a conventional defect compensator for a solid-state image pickup device. A signal output from a pre-amplifier 1 is input to a clamp part 2, a delay driver part 3 and a video driver part 4. The clamp part 2 fixes the output signal from the pre-amplifier 1 at a constant reference level. A signal output from the delay driver part 3 is input to DC level shift part 5 and; delay part 6. The delay part 6 delays an output signal of the delay driver part 3 for a certain time period. A defect detector 7 detects output signals from the delay part 6 and the DC level shift part 5, and outputs a control pulse to compensate a defect. A pulse adjustment part 8 delays the output pulse of the defect detector 7 for a certain time period and adjusts the width of the output pulse. The normal signal applied to the video driver part 4 is input to a level shift part 9. An image signal correction part 10 is controlled by the control signal of the pulse adjustment part 8 upon receipt of the output signal from the level shift part 9. A main video gate 11 is also controlled by the control signal of the pulse adjustment part 8. A video line driver part 12 outputs a signal selected by the control signal of the pulse adjustment part 8.
The operation of the conventional defect compensator for a solid-state image pickup device arranged as described above will now be explained. As shown in FIG. 1, the pre-amplifier 1 amplifies an image signal input from a charge coupled device (CCD) and the clamp part 2 fixes the amplified signal at a constant reference level.
The output signal of the pre-amplifier 1 is applied to the delay driver part 3 and the video driver part 4, respectively. The signal output from the delay driver part 3 is delayed for about 115 ns by a delay clock at the delay part 6.
The delayed signal from delay part 6 and delayed signal and the level shifted signal from the DC level shift part 5 are input to the defect detector 7 to be compared with each other. If the signal difference between the two signals is larger than a reference signal, the defect detector 7 generates an output trigger pulse.
The trigger pulse is delayed by the pulse adjustment part 8 for a certain time period to adjust the width of the pulse. Then, the trigger pulse is input to the image signal correction part 10 and the main video gate 11, respectively.
As a result, the defect is determined by comparing neighboring pixels one another. That is, when two pixels exist on the same chip, the video output signal for real time is compared with the delayed signal to determine the defect.
When the delayed signal is the same as the current video output signal or has little difference from the current video output signal, the current video output signal is finally output. When the delayed signal is larger than the current video output signal, a signal following to the current video signal is finally output. Therefore, the output of the video line driver part 12 is selectively controlled by the output trigger pulse of the defect detector 7.
However, the conventional defect compensator has several problems.
First, the configuration of hardware is complicated since the defect is compensated outside CCD device. This causes the defect compensator to be sensitive to noise.
Second, the resolution is degraded since the level difference for only two pixels, i.e., the current pixel and the following pixel, is detected and compared.